Field
The present disclosure relates to a telecommunications device comprising an electrical-balance duplexer (EBD) circuit, and a tunable impedance network and method for tuning a tunable impedance network that can be used with the EBD circuit or in other applications.
Description of the Related Technology
An electrical-balance duplexer (EBD) is a tunable RF frontend concept that addresses some of the key challenges of 4G and 5G mobile systems. The basic principle of the EBD is shown in FIG. 1. Duplexer isolation is achieved when the signals in paths 1 and 2 cancel and prevent the TX signal from appearing at the RX port. This cancellation is achieved by balancing the antenna port's impedance ZANT with a tunable on-chip impedance ZBAL, hence the name ‘electrical-balance’.
Wireless devices now support an increasing number of 4G FDD bands, and a tunable integrated solution like this could potentially replace several fixed-frequency filters and switches. The EBD is also attractive for 5G in-band full-duplex (FD) communication systems. Whereas a filtering-based duplexer cannot isolate the TX and RX ports for the special case where fTX=fRX, the EBD's signal cancellation approach still works.
However, the entire EBD concept depends on the capability to tune ZBAL into balance with ZANT. This needs to happen not just at a single frequency, but across the entire bandwidth of both the TX and RX channels. Additionally, the impedance characteristic of the antenna will vary significantly over time due to interaction with the user and environment. Designing a ZBAL that is generic enough to work with real cellular antennas is therefore a challenge.
Although many papers have reported EBD isolation levels of more than 40 dB across bandwidths ranging from 10's to 100's of MHz, these are all for highly selective ‘best-case’ scenarios which are not applicable to real world conditions. For example, a tunable integrated duplexer with dual-frequency tuning is known in the art, where the provided coverage is limited to selective best-cases.